Shia scholar Saeed Akhtar Rizwi puts forward the usual shia ranting about Fadak in his book, "Fadak".
He says,
"Fadak became a personal property of the Prophet; and he managed it himself.7
Then another 'Aya came:-
"Andgive to the near of kin his due ..." (Qur'an, 17:26).
The Prophet asked Jibril the meaning of this revelation. He said: Give Fadak to Fatimah; it will be a source of income to her and her children.8
The Prophet gave Fadak to Fatimah; and she was using it as her own property; her agent was there to look after her interests. This continued till the Prophet died and Abu Bakr took the possession of Fadak by force.
Now Fatimah protested against this usurpation of her property, saying that the Prophet had given it to her. Abu Bakr asked her to produce witnesses to prove it.
Now Fatimah was already in possession of the property; and according to the Islamic principles, possession itself is a sufficient proof of ownership. If Abu Bakr claimed that property for himself or for Muslim nation, then it was he, as claimant, who should have produced witnesses to support his claim. But he put the onus of proof on Fatimah, disregarding Islamic Law.
Again, as he was a claimant, he should not have judged the case himself. But he did not care for judicial niceties so long as his purpose was served.
Anyhow, Fatimah brought 'Ali and Umm Ayman (widow of Zaid b. Haritha). Abu Bakr said that there should be either two males or one male and two female witnesses.9
Now in family matters- and gift of a father to his daughter is a family matter - only one witness is enough; but Abu Bakr conveniently forgot it. Also Islam accepts one witness coupled with the oath of the claimant as a sufficient proof.10
Fatimah was obliged to bring other witnesses, among them her two sons, Hasan and Husain and one woman, Asma' d/o 'Umais (wife of Abu Bakr himself).
Now there were more witnesses than the minimum required. So Abu Bakr started discrediting all the witnesses:-
A) 'Ali, Hasan and Husain were Fatimah's husband and sons, and they were liable to be moved by self-interest.
Remember that Fatimah, 'Ali, Hasan and Husain were the only ones who were selected by the Prophet to prove his truth against the Christians of Najran - who were to say ''Amen'' to the prayer of the prophet seeking curse of Allah "against the liars:'
They were the only people alive at that time who were purified by Allah from all sins and mistakes.
And there is not a single Muslim in the world who can say that they could tell lies.
But Abu Bakr rejected their evidence explicitly saying that their evidence was motivated by self-interest - in other words, they were lying!!
B) Asma' d/o 'Umais was previously married to Ja'far, brother of 'Ali; and therefore, she would support the claim of Banu Hashim.
He forgot that she was his wife and therefore her evidence against his views was more telling.
And, by the way, is it necessary that a witness should not be a friend of the party for whom he is appearing - that only the evidence given by an enemy should be accepted?
C) Umm Ayman was a non-Arab and she could not speak Arabic fluently. (Umm Ayman was a slave-girl of 'Abdullah, father of the Prophet. The Prophet had inherited her, married her to Zaid b. Haritha and, according to the Prophet she was one of "the people of virtue': "people of Paradise'
Does it mean that only Arabic-speaking people can be accepted as witness? Or only Arabs are truthful and trustworthy?
This ruthlessness of the Khalifa prevented others to come forward and give evidence on behalf of Fatimah. When the Khalifa had no hesitation in degrading and insulting 'Ali and his sons, how could they be sure that their honour would not be tarnished if they appeared to support Fatimah?"
https://www.al-islam.org/fadak-allamah-sayyid-saeed-akhtar-rizvi/fadak
The problem with this shia argument is that if Fadak was already in the hands of Fatima (r.a), it should never have been difficult for her to bring witnesses other than her husband and her sons and Umm Ayman. Why was she not bringing other witnesses who were not amongst her kins.
For example, Abu Saeed Khudri. He was the right man, as according to shia, he narrated the tradition that when the particular ayah already mentioned in the shia argument above was revealed, the prophet (s) gifted Fadak to his daughter. But he was never brought forward as a witness.
Another witness could have been Ibn Abbas, because an other tradition of fadak being gifted is attributed to him. None of these two great companions are brought forward as witnesses.
The third witness could have been the person who were managing Fadak on behalf of Fatima as according to Shias, Fadak was already in her possession.
This makes the whole issue ambiguous and reveals the falsehood in the whole story of Fadak being gifted.